Control valves are commonly used to control fluid flow through a pipe. As known to those skilled in the art, a control valve regulates the rate of fluid flow as an actuator changes the position of a moveable operator or valve trim within the control valve. Certain process fluids may be very corrosive to the control valve. To counteract the effects of the corrosive process fluid, control valve manufacturers may select special materials that are generally impervious to the corrosive effects of the process fluid. For example, nickel alloy UNS N10276 is known to have superior corrosion resistance to a wide range of corrosive agents. Using special corrosion resistant alloys, particularly in valve bodies, can be cost prohibitive for less expensive valves like butterfly-style control valves. Valve manufacturers generally address this cost issue by supplying the valve body with a corrosion resistant, non-conductive liner.
The advantage of a lined valve is that the valve body is not wetted by the process fluid and therefore can be made from less expensive materials when used in corrosive applications. Valve body liners are typically made from elastomers such as ethylene propyl terpolymer (EPDM). These elastomers are typically non-conductive and have dielectric properties. As known to those skilled in the art, the dielectric material substantially insulates the valve trim from the valve body effectively creating a capacitor that may store an electrostatic charge. Additionally, numerous control valve applications do not use packing materials, seals, and/or guide bushings that have conductive properties. Therefore, if the valve trim is not positively grounded to the valve body with a shared electrical connection, fluid flow through the valve body and across the valve trim may create an electrostatic charge transfer that can accumulate similar to a capacitor accumulating an electrostatic charge. The accumulating charge can establish a potential difference of several thousand volts between the valve body and valve trim. As is known, when the accumulated charge exceeds the breakdown voltage of the dielectric or insulator, an arc may result. Also, if a momentary discharge path is created between the valve body and the valve trim, for example a wrench being used during routine maintenance, an arc could be struck. As a result, numerous industry standards and governmental regulations require that equipment used in an explosive atmosphere shall be designed to operate safely in that atmosphere. The equipment, including mechanical devices such as valves, must be free of sources that may lead to ignition of the surrounding atmosphere.
Typical solutions include the use of external grounding straps between valve components and conductive packing. Due to cost, however, these solutions are not applicable to all control valve designs. External straps can also be severed during operation subsequently creating an ignition source at the control valve. Lastly, known to those skilled in the art, the external surfaces of valve bodies and actuators are typically painted with a powder-coated paint that provides an extremely durable, scratch resistant coating that also functions as an insulator. Therefore, conventional assemblies require manual removal of the paint from conductive surfaces to provide a shared electrical connection between the valve components. In a manufacturing operation, these manual operations are time consuming and expensive.